The field of the invention relates to prevention of frost build-up within a freezer compartment.
One common approach of cooling freezers and refrigerators is to use a tube and fin evaporator. In a conventional configuration, the tube and fin evaporator is positioned in a small chamber external to the freezer and refrigerator compartments, and a fan is used to recirculate air from the respective compartments through ducts past the evaporator. Typically, the fan and the compressor are controlled by the temperature setting of the freezer, and the temperature of the refrigerator is controlled by a manual or thermostat controlled throttle in the air duct communicating therewith. As is well known, it is undesirable to have ice accumulate on the outside of the evaporator because it causes the efficiency of the thermal transfer to decrease. To eliminate the ice or frost, the evaporator typically has an electric heater that is periodically energized during compressor off-time to melt the ice.
One problem with the above described evaporator configuration is that it normally adds at least 2 inches to the height of the refrigerator/freezer. Stated differently, for a given refrigerator/freezer height, approximately one cubic foot of otherwise usable space may be lost to the evaporator chamber, fan, and associated ducting. A smaller tube or fin evaporator could be used in the above-described refrigerator/freezer to reduce space but it would increase refrigerator/freezer overall energy consumption.
Another approach of cooling freezers is to use a plate evaporator system. Rather than cooling by circulating air through ducts, the refrigerator and freezer walls themselves are partially fabricated from aluminum containing evaporator tubes. The wall surfaces become very cold and heat is transferred to them substantially by thermal radiation. This approach has an important advantage of saving space due to the elimination of the evaporator chamber, fan, and ducts. Also, the unit runs quieter. Further, elimination of fans generally saves over 1/2 Kw/hr/day in energy. The reliability is also increased because fewer components are used.
However, a plate evaporator system has a serious disadvantage in that ice or frost is much more difficult to remove than with the above described tube-and-fin evaporator. Because the plate evaporator actually makes up at least part of the walls of the freezer compartment, the entire freezer compartment rather than the external evaporator, must be raised above 32.degree. F. to remove the ice. To do this, the freezer is generally turned off for some period of time. Not only is this procedure bothersome, but it also decreases the operating efficiency of the plate evaporator system.